A Novel Onboard-gateway-based Mechanism to Improve TCP Performance in Aeronautical Satellite Networks

The IP-based networks on aircraft serve to support Internet services via satellites. However, in aeronautical satellite hybrid net- works,the TCP protocol performance often deteriorates due to improper decreases and slow recovery of the congestion window. This paper proposes a window size determination and notification mechanism, onboard-gateway-based mechanism (OGBM), which is based on the onboard gateway in the networks on aircraft. A cross-layer approach is adopted by the onboard gateway to obtain the satellite link bandwidth information. And then, by the gateway, through changing the receiver’s advertised window field in ACK packets, TCP sources are notified of the window size of each TCP source calculated on the ground of bandwidth delay product and flow numbers. The mechanism is able to avoid improper changes of TCP window and serve multiple users. Simulation results show that the mechanism with the fairness index close to 1 improves TCP performance in aeronautical satellite networks.     

无人机模拟训练系统中的实时飞行仿真

为了降低无人机的试飞成本,提高操纵手的技能,设计了一种模拟训练系统。介绍了该模拟训练系统的特点和构成,着重对系统中实时飞行仿真的各模块设计方法进行了研究。在DOS操作系统中用C语言实现飞行仿真软件,并讨论了软件实现中的模态切换等关键问题。通过飞行剖面仿真实验,证明该仿真系统可靠性高、实时性好。     

基于数据库技术的故障诊断知识库管理系统设计

为解决传统大型复杂系统故障诊断专家系统中存在的知识库庞大、难于维护管理的问题,结合数据库技术设计了一套基于Windows平台的知识表示和知识库管理系统。该系统充分利用了数据库技术,实现了对知识库中知识的存储、添加、删除、修改和查询以及编辑过程中的一致性、完备性和冗余性要求,通过将该系统应用到运载火箭测试发射中的故障诊断专家系统中,一定程度上实现了知识处理的自动化,为运载火箭故障诊断专家系统的开发和运用奠定了重要基础。     

GRACE gravity field modeling with an investigation on correlation between nuisance parameters and gravity field coefficients

The GRACE (Gravity Recovery And Climate Experiment) monthly gravity models have been independently produced and published by several research institutions, such as Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL), Centre National d’Etudes Spatiales (CNES) and Delft Institute of Earth Observation and Space Systems (DEOS). According to their processing standards, above institutions use the traditional variational approach except that the DEOS exploits the acceleration approach. The background force models employed are rather similar. The produced gravity field models generally agree with one another in the spatial pattern. However, there are some discrepancies in the gravity signal amplitude between solutions produced by different institutions. In particular, 10%–30% signal amplitude differences in some river basins can be observed. In this paper, we implemented a variant of the traditional variational approach and computed two sets of monthly gravity field solutions using the data from January 2005 to December 2006. The input data are K-band range-rates (KBRR) and kinematic orbits of GRACE satellites. The main difference in the production of our two types of models is how to deal with nuisance parameters. This type of parameters is necessary to absorb low-frequency errors in the data, which are mainly the aliasing and instrument errors. One way is to remove the nuisance parameters before estimating the geopotential coefficients, called NPARB approach in the paper. The other way is to estimate the nuisance parameters and geopotential coefficients simultaneously, called NPESS approach. These two types of solutions mainly differ in geopotential coefficients from degree 2 to 5. This can be explained by the fact that the nuisance parameters and the gravity field coefficients are highly correlated, particularly at low degrees. We compare these solutions with the official and published ones by means of spectral analysis. It is found that our solutions are, in general, consistent with others in the spatial pattern. The water storage variations of the Amazon, Chari and Ganges river basins have also been computed. The variations computed with the NPARB approach are closer to those produced by JPL and DEOS solutions, while the variations produced with the NPESS approach are in good agreement with those produced by the CSR and GFZ solutions. A simulation study is implemented with considering realistic noise and low-frequency error. The two approaches are used to recover the true model. The NPESS solution appears closer to the true one. Therefore we are inclined to estimate the nuisance parameters simultaneously with the geopential coefficients.     

抗振晶体振荡器的仿真设计CSCD

本文介绍了利用仿真软件进行抗振晶体振荡器设计的方法,通过建立晶体振荡器结构仿真模型,对其力学特性进行深入细致的分析,并在此基础上对比分析减振材料的剪切模量和被减振物质量对晶体振荡器抗振性能的影响,优化晶体振荡器减振结构。然后,根据仿真设计制做了抗振晶体振荡器,并进行了随机振动试验。结果表明,试验现象与仿真结果基本一致,验证了仿真分析的有效性,且振动下晶体振荡器相位噪声达到-145d Bc/Hz@1k Hz,极大地提高了晶体振荡器的抗振性能。     

飞行器太阳能源计算方法CSCD

介绍了空间飞行器典型电源系统组成,通过对影响太阳能源输出的各项参数因素分析,提出了空间飞行器太阳能源计算方法,该方法包括由功率计算所需太阳阵面积的公式和由太阳阵面积计算输出功率的公式,达到了准确计算太阳能源的效果,解决了以往空间飞行器太阳能源估算误差大,在总体回路设计中电源参数难以闭环的问题。     

紊流发生器特性和流场的模拟调节

本文探讨了轴对称紊流发生器总压畸变流场的不稳定性,根据流场低压区的时钟位置和大小是否随时间而变化,可分为稳定型和非稳定型两种.对于稳定场,畸变指数测量的重复性较好,非稳定场则较差.文中还介绍了一种简单而有效的流场模拟调节方法.     

“AP/HTPB/Al/催化剂”推进剂燃烧模拟计算方法

本文以我们在文献[1～4]中提出的“AP/HTPB/Al”推进剂燃烧模型为基础,首先讨论了催化剂作用部位与推进剂燃速、压力指数变化的关系,然后引入一个催化剂作用因子B.并以二茂铁系列催化剂为例,对模型中的几个与二茂铁催化剂作用部位相连系的反应动力学参数作“催化作用因子”校正,计算研究了四种二茂铁催化剂用量对燃速、压力指数的影响规律.计算结果与实验符合得很好,相对误差均小于±10%,证明本文提出的模拟计算方法具有较高的可靠性.     

基于液晶光阀的动态红外场景仿真研究

介绍了基于液晶光阀的动态红外场景仿真系统构成,分析了液晶光阀的波长变换和空间调制机理。对反映红外场景仿真效果主要因素(光谱输出特性、时间响应特性和空间分辨力)进行了理论分析和研究。利用优化设计液晶光阀参数构建的动态红外场景仿真样机,测量其光谱输出特性、时间响应特性和空间分辨力,结果表明,仿真系统的输出光谱可覆盖中波和长波红外波段,可实现帧频70Hz,系统空间分辨力优于10 lp/mm(受红外光学系统和红外热像仪分辨力限制)。